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724 Chapter 21
Copyright © 2017 Pearson Education, Inc.
The least negatively charged fragment will be eluted first, and the most negatively charged fragment
will be eluted last:
A
7
D
7
C
7
B
A
Gly-Ala-Asp-Ala-Leu-Pro-Gly-Ile-Leu-Val-Arg
overall charge
=
0
+
-
+ -
B
Asp-Val-Gly-Lys-Val-Glu-Val-Phe-Glu-Ala-Gly-Arg
overall charge
=
-
3
+ -
-
-
-
+ -
C
Ala-Glu-Phe-Lys-Glu-Pro-Arg
overall charge
=
-
2
+
-
-
-
+
-
D
Leu-Val-Met-Lys-Val-Glu-Gly-Arg-Pro-Val-Ala-Ala-Gly-Leu-Trp
overall charge
=
-
1
+
-
-
+
-
66.
First, mark off where the chains would be cleaved by chymotrypsin (C-side of Phe, Trp, Tyr).
Val-Met-Tyr Ala-Cys-Ser-Phe Ala-Glu-Ser
Ser-Cys-Phe Lys-Cys-Trp Lys-Tyr Cys-Phe Arg-Cys-Ser
Then from the fragments given, you can determine where the disulfide bridges are in the original intact
peptide. For example, “Fragment 2” has two Phe, two Cys, and one Ser. Therefore, the first and fourth
fragments of the second row must be connected by a disulfide bond. Fragment “5” provides the evidence
for the disulfide bond between the two chains.
Val-Met-Tyr-Ala-Cys-Ser-Phe-Ala-Glu-Ser
S
S
S S
Ser-Cys-Phe-Lys-Cys-Trp-Lys-Tyr-Cys-Phe-Arg-Cys-Ser
67.
The methyl ester of phenylalanine rather than phenylalanine itself should be added in the second peptide
bond-forming step because if esterification of phenylalanine is done after amide bond formation, both the
carboxyl group of phenylalanine and the
g
-carboxyl group of aspartate can be esterified. Both the carboxyl
group of phenylalanine and the
g
-carboxyl group of aspartate can be activated by DCCD. Therefore, some
product will be obtained in which the amide bond is formed with the
g
-carboxyl group of aspartate rather
than with the
a
-carboxyl group.